This invention relates to polymeric compositions made from arylcyclobutene containing monomers and methods for preventing autoxidation of said polymers.
Arylcyclobutene monomeric compositions are useful in preparing thermoset and thermoplastic polymeric compositions. Such polymeric compositions are highly desirable because they exhibit hydrophobicity, excellent thermal stability, chemical resistance and electrical insulative properties. Such polymeric compositions typically can exhibit thermal degradation temperatures above 300.degree. C., are insoluble in many organic solvents and in water and have dielectric constants of less than 3.0 at 1 MHz. Therefore, they find uses as films, coatings, adhesives and as interlayer dielectrics in multichip modules and other multilayer electronic circuits.
Johnson et al. disclose in IEEE Transactions On Components, Hybrids, and Manufacturing Technology, Vol. 13, No. 2, June, 1990, that a polymer of ##STR1## 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3-tetramethyld i siloxane (hereinafter DVS), available as a partially polymerized solution in mesitylene from The Dow Chemical Company as XU13005.02L (hereinafter partially thermally polymerized DVS or DVS prepolymer) may be used as an interlayer dielectric to construct thin film multichip modules. The partially thermally polymerized DVS may be applied by spin coating a solution of a prepolymer onto a substrate, evaporating the solvent and then polymerizing by heating to 250.degree. C. for one hour in nitrogen. Catalysts and/or initiators are not required for the polymerization.
When exposed to air arylcyclobutene polymers undergo oxidation. At elevated temperatures the oxidation is accelerated. When the polymer oxidizes, its electrical insulating properties are degraded. Oxidation may lead to a yellow discoloration of the polymer, and in severe cases to an amber color even in thin films.
One may encapsulate the arylcyclobutene polymer by forming an oxygen barrier around it. However, this adds costly steps to a fabrication process. Barrier coatings are also subject to breakage and/or cracking, particularly under thermal cycling, which leads to loss of the barrier protection.
To preserve optical clarity and important electrical properties such as low dielectric constant and low water uptake without the use of hermetic packaging or barrier coatings, it would be advantageous to have an arylcyclobutene polymer composition that is less susceptible to oxidation when exposed to air.